Corona-resistant self-lubricating magnet wire

ABSTRACT

A corona-resistant self-lubricating magnet wire includes a conductor wire, an insulator sheath wrapped around the conductor wire, and an outer layer of a lubricating material coated on the sheath. The lubricating material is composed of a polyamideimide resin and a polymeric material selected from a group consisting of polyethylene and Teflon.

BACKGROUND OF THE INVENTION

[0001] 1. Field of the Invention

[0002] This invention relates to a corona-resistant self-lubricating magnet wire, more particularly to a corona-resistant self-lubricating magnet wire coated with a lubricating material.

[0003] 2. Description of the Related Art

[0004] Enamelled materials are widely used in induction coils of motors, such as high frequency high voltage motors, for protecting the enamelled coils from damage due to corona discharge that occurs during a change in frequency upon adjusting the motor speed.

[0005] U.S. Pat. No. 4,546,041 discloses a corona-resistant wire enamel composition that contains a polyesterimide resin and from about 1% to about 35% by weight of dispersed alumina particles of a finite size less than about 0.1 micron. The entire disclosure of the patent is incorporated herein by reference.

[0006]FIG. 1 illustrates a commercially available enamelled wire 1 that has corona-resistant characteristics and that includes a conductor wire 11 of copper, and an insulating sheath that surrounds the conductor wire 11. The sheath includes two insulating layers 12, 13 of thermal-resistant materials coated on the conductor wire 11, a corona-resistant layer 14 of a corona-resistant material disposed between the insulating layers 12, 13, and an outer layer 15 of a wax material coated on the insulating layer 13. The insulating layers 12, 13 are respectively made from modified polyesterimide and polyamideimide. In order to provide the corona-resistant characteristics, the corona-resistant material normally contains a resin material, such as polyamideimide, and an inorganic filler, such as aluminum oxide. The aforesaid conventional enamelled wire 1 is disadvantageous in that the sheath is relatively fragile due to the presence of the filler and thus tends to break upon winding into a motor induction coil. Moreover, as illustrated in FIG. 2, although lubricated with a wax material to smooth the winding operation, uneven winding of the enamelled wire 1 on a core body 2 can still occur due to a relatively high friction force between contacting faces of adjacent loops 16, 16′ of the enamelled wire 1 when the winding operation is performed via a winding machine (not shown).

SUMMARY OF THE INVENTION

[0007] Therefore, it is an object of the present invention to provide an insulated wire that is capable of overcoming the aforementioned drawbacks.

[0008] According to the present invention, a magnet wire comprises: a conductor wire; an insulator sheath wrapped around the conductor wire; and an outer layer of a lubricating material coated on the sheath. The lubricating material is composed of a polyamideimide resin and a polymeric material selected from a group consisting of polyethylene and Teflon.

BRIEF DESCRIPTION OF THE DRAWINGS

[0009] In drawings which illustrate an embodiment of the invention,

[0010]FIG. 1 is a cross-sectional view of a conventional enamelled wire;

[0011]FIG. 2 is a cross-sectional view of the enamelled wire of FIG. 1 when wound on a core body;

[0012]FIG. 3 is a cross-sectional view of a corona-resistant self-lubricating magnet wire embodying this invention;

[0013]FIG. 4 is a schematic view to illustrate measurement of friction force of a sliding block that is wound with the magnet wire of FIG. 3, on a friction force measuring device; and

[0014]FIG. 5 is a cross-sectional view of the magnet wire of FIG. 3 when wound on a core body.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT

[0015]FIG. 3 illustrates a corona-resistant self-lubricating magnet wire 3 embodying this invention for applications, such as winding into induction coils for high frequency high voltage motors (not shown). The magnet wire 3 includes a conductor wire 31, an insulator sheath 30 wrapped around the conductor wire 31, and an outer layer 34 of a lubricating material coated on the sheath 30. The lubricating material of the outer layer 34 is composed of a polyamideimide resin and a polymeric material selected from a group consisting of polyethylene and Teflon, such as tetrafluoroethylene and hexafluoropropylene.

[0016] Preferably, the polymeric material is polyethylene having a molecular weight in a range of from 1000 to 50000. More preferably, the polymeric material is polyethylene having a molecular weight in a range of from 2000 to 10000.

[0017] Preferably, the weight ratio of the polyamideimide resin to the polymeric material of the lubricating material is in a range of from 100:0.5 to 100:10. More preferably, the weight ratio of the polyamideimide resin to the polymeric material of the lubricating material is in a range of from 100:1 to 100:6.

[0018] The sheath 30 can be made from a single layer of any one of conventional enamelled compositions. In the preferred embodiment, the sheath 30 includes a two-layer structure (see FIG. 3), which has a corona-resistant layer 32 of a corona-resistant resin that is coated on the conductor wire 31, and an insulating layer 33 of a thermal-resistant resin that is coated on the corona-resistant layer 32. The outer layer 34 of the lubricating material is coated on the insulating layer 33.

[0019] The conductor wire 31 is made from a metal material selected from a group consisting of copper and aluminum. The corona-resistant resin is preferably made from a modified polyesterimide which is commercially available under the trade name of VOLTRON, E-3599, etc., from DuPont Corporation. The thermal-resistant resin is preferably polyamideimide.

[0020] Having the general nature of the invention set forth above, the following Examples and Comparative Examples are presented in order that the invention may be more readily understood.

[0021] Static Friction Force Test

EXAMPLES 1 TO 13 AND COMPARATIVE EXAMPLE 1

[0022] Referring to FIG. 4, in combination with FIG. 3, the static friction force test was carried out using a friction force measuring device 5 which includes a fulcrumed lever 511 wound with the magnet wire 3 of this invention for Examples 1 to 13 or the conventional wire for the Comparative Example 1, a scale unit 52 with an indicia 521 thereon, a pointer 522 associated with the lever 511 for pointing to the indicia 521, and a sliding block 53 placed on the lever 511 and wound with a wire that is the same as that wound on the lever 511. During the test, the lever 511 is gradually inclined to a position so as to permit the sliding block 53 to overcome the static friction force and to start moving. The static friction force between contacting faces of the sliding block 53 and the lever 511 thus measured is represented by the indicia 521 pointed by the pointer 522 at the aforesaid postion. A higher number of the indicia 521 represents higher static friction force therebetween.

[0023] Examples 1 to 13 respectively represent different weight ratios of polyamideimide resin to the polymeric material of the lubricating material of the magnet wire 3 of this invention. Comparative Example 1 represents the aforementioned conventional enamelled wire 1 of FIG. 1.

[0024] The static friction forces thus measured in Examples 1 to 13 and the Comparative Example 1 are listed in Table 1. TABLE 1 Lubricating material Polyamide- Polyethylene, part imide, M.W. = M.W. = M.W. = M.W. = Teflon, Friction Example part 2000 3000 4000 10000 part force  1 100 1 — — — — 0.09-0.12  2 100 3 — — — — 0.08-0.09  3 100 6 — — — — 0.07-0.08  4 100 — 1 — — — 0.08-0.09  5 100 — 3 — — — 0.07-0.08  6 100 — 6 — — — 0.05-0.06  7 100 — — 1 — — 0.09-0.10  8 100 — — 3 — — 0.08-0.09  9 100 — — 6 — — 0.07-0.08 10 100 — — — 1 — 0.08-0.09 11 100 — — — 3 — 0.07-0.08 12 100 — — — 6 — 0.05-0.06 13 100 — — — 1 0.05-0.06 Comparative — — — — — — 0.09-0.12 Example 1

[0025] The result of the static friction force test shows that all of the Examples 1 to 13 have a lower static friction force than that of the Comparative Example 1, and that a higher amount of polyethylene in the lubricating material tends to reduce the static friction force. FIG. 5 illustrates the magnet wire 3 of this invention being capable of evenly winding into loops 35 around a core body 6 due to a lower static friction force thereof. As a consequence, the uneven winding drawback as encountered in the prior art can be eliminated.

[0026] Corona-Resistant and Thermal-Resistant Test

EXAMPLES 14 AND 15 AND COMPARATIVE EXAMPLE 2

[0027] The corona-resistant and thermal-resistant test was carried out by applying 100 meters of the magnet wire 3 of this invention (Examples 14 and 15) or the aforesaid conventional wire (Comparative Example 2) to a high frequency high voltage motor, and by exposing the magnet wire 3 or the conventional wire to a temperature of 190° C. , a frequency of 15 KHz, and a corona voltage of 1100 V to observe the life of the magnet wire 3 or the life of the conventional wire under such conditions. The lubricating materials used in the Examples 14 and 15 are respectively a mixture of polyamideimde and polyethylene and a mixture of polyamideimide and Teflon. The corona-resistant resin and the thermal-resistant resin used in the magnet wire 3 of Examples 14 and 15 are respectively polyesterimide and polyamideimide. The test result is listed in Table 2. TABLE 2 Example Life, hours 14 186 15 186 Comparative Example 2 66.5

[0028] The result of the test shows that the use of the corona-resistant layer 32 of polyesterimide and the insulating layer 33 of polyamideimide for the sheath greatly improves the corona-resistant and the thermal-resistant properties of the magnet wire.

[0029] With the invention thus explained, it is apparent that various modifications and variations can be made without departing from the spirit of the present invention. It is therefore intended that the invention be limited only as recited in the appended claims. 

We claim:
 1. A magnet wire comprising: a conductor wire; an insulator sheath wrapped around said conductor wire; and an outer layer of a lubricating material coated on said sheath, said lubricating material being composed of a polyamideimide resin and a polymeric material selected from a group consisting of polyethylene and Teflon.
 2. The magnet wire of claim 1, wherein the weight ratio of said polyamideimide resin to said polymeric material of said lubricating material is in a range of from 100:0.5 to 100:10.
 3. The magnet wire of claim 1, wherein the weight ratio of said polyamideimide resin to said polymeric material of said lubricating material is in a range of from 100:1 to 100:6.
 4. The magnet wire of claim 1, wherein said sheath includes a corona-resistant layer of a corona-resistant resin that is coated on said conductor wire, and an insulating layer of a thermal-resistant resin that is coated on said corona-resistant layer.
 5. The magnet wire of claim 4, wherein said corona-resistant resin is made from a modified polyesterimide.
 6. The magnet wire of claim 4, wherein said thermal-resistant resin is polyamideimide.
 7. The magnet wire of claim 1, wherein said conductor wire is made from a metal material selected from a group consisting of copper and aluminum.
 8. The magnet wire of claim 1, wherein said polymeric material is polyethylene having a molecular weight in a range of from 1000 to
 50000. 9. The magnet wire of claim 1, wherein said polymeric material is polyethylene having a molecular weight in a range of from 2000 to
 10000. 